People are surprised when they discover that gangs in otherwise sedate and often upscale Santa Monica and West L.A. have been warring for years.

But the death toll has been mounting quietly for decades, and as recently as last summer a Santa Monica murder led to the arrest of three suspects who police say are affiliated with West L.A.'s Sotel gang.

Last night, Santa Monica police claimed victory in yet another homicide tied to the rivalry:

The department announced that West L.A.'s Jose Zapien, who was 18 when he was arrested in 2007, has been convicted for the 2006 murders of Santa Monica residents Eduardo Lopez and Miguel Martin -- as well as the attempted murders of 12 other people.

Cops say Zapien was with other suspects on Feb. 28, 2006, when he opened fire on "a group of young teenagers" in Santa Monica, killing Lopez, who was only 15. Eight other suspects with Zapien were arrested following the attacks.

The teen was on the Santa Monica High School football and baseball teams, was well-liked, and was killed "at the prime of his life," according to a police statement.